The present invention relates to a novel naphthoquinone derivative, and an electrophotosensitive material using the same, which is used in image forming apparatuses such as copying machine, facsimile, laser beam printer and the like.
In the above image forming apparatuses, electrophotosensitive materials of various materials are used. The one is an inorganic photoconductor using an inorganic material such as selenium in a photosensitive layer and the other one is an organic photoconductor (OPC) using an organic material in a photosensitive layer. Among them, the organic photoconductor has widely been studied because of a lot of merits such as cheap price, high productivity and no environmental pollution in comparison with the organic photoconductor.
As the organic photoconductor, a multi-layer type (so-called function-separating type) photoconductor comprising an electric charge generating layer and an electric charge-transferring layer, which are laminated, has exclusively been known, but a so-called single-layer type photoconductor wherein an electric charge generating material and an electric charge-transferring material are dispersed in a single photosensitive layer, has also been known.
Those having high carrier mobility are required as the electric charge-transferring material used in these photoconductors. However, almost all of electric charge-transferring materials having high carrier mobility show hole transferring properties. Therefore, the organic photoconductor put into practical use is limited to a negative charging type multi-layer type organic photoconductor provided with an electric charge-transferring layer at the outermost layer in view of the mechanical strength. However, since the negative charging type organic photoconductor utilizes negative-polarity corona discharge, a large amount of ozone is generated and, therefore, problems such as environmental pollution, deterioration of photoconductor, etc. arise.
Therefore, in order to solve these problems, it has been studied to use an electron transferring material as the electric charge-transferring material. In Japanese Patent Laid-Open Publication No. 1-206349, there is suggested that a compound having a diphenoquinone structure or a benzoquinone structure is used as the electron transferring material for electrophotosensitive material.
In Japanese Patent Laid-Open Publication No. 6-110227, there is suggested that a compound having a benzoquinone structure or a naphthoquinone structure is used as the electron transferring material for electrophotosensitive material.
However, since it is difficult to perform matching between a conventional electron transferring materials such as diphenoquinone derivative, benzoquinone derivative, naphthoquinone derivative, etc. and the electric charge generating material, the injection of electrons from the electric charge generating material into the electron transferring material is insufficient. Furthermore, since the electron transferring material has poor compatibility with a resin binder and a hopping distance becomes longer, electron movement at low electric field is dull. Accordingly, a photoconductor containing a conventional electron transferring material had a problem such as high residual potential and low sensitivity, as is apparent from a photosensitivity test described in the following Examples.
As described above, almost all of practical organic photoconductors have a multi-layer type photosensitive layer at present, whereas a photoconductor having a single-layer type photosensitive layer has a simple structure and can be easily produced, and has a lot of merits in view of inhibition of damage in coating of the layer, improvement in the optical characteristics, etc.
And besides, regarding such a photoconductor having a single-layer type photosensitive layer, one photoconductor can be used in both the positive charging and the negative charging types by using the electron transferring material in combination with the hole transferring material, and there is a possibility of increasing applications of the photoconductor. However, since a conventional transferring material has a problem of inhibiting transferring of electrons and holes due to the mutual interaction with the hole transferring material, such a photoconductor having a single-layer type photosensitive layer has not been put to practical use, widely.